1. Technical Field
The invention relates to chairs, particularly to back tilt adjustment of chairs.
2. Related Art
Some office chairs are provided with a back tilt adjustment function. Such a function is typically accomplished by a spring between a cushion and a back. However, this spring tends to elastic fatigue.
Some chairs adopt a flexible tilt adjustment structure as shown in FIG. 1. The structure is fixed to a seat 61 through an adjustment rod 60. An end of the adjustment rod 60 connects a driving block 62. The seat 61 is provided with a transmission rod 63. The transmission rod 63 is pivotally connected to the driving block 62. A spring 64 is passed by the transmission rod 63. The seat 61 is provided with a sway element 66 connected to a back. The sway element 66 is pushed by the spring 64. Thus the back can be adjusted by moving the transmission rod 63 flexibly pushed by the spring 64.
In above structure, rotating the adjustment rod 60 to move the transmission rod 63 by hand needs a larger force. This causes inconvenience in operation. The adjustment rod 60 and transmission rod 63 need a link set 65 to change the direction of force. When the link set 65 has jammed, the whole adjustment structure cannot work. Furthermore, the single-sided transmission from the link set 65 to the transmission rod 63 is easy to be unbalanced. This will cause damage of the transmission rod 63.